immunity

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Questions and Answers

What is the primary function of memory B cells following a pathogenic encounter?

They increase inflammation in response to future infections.

They remain in the body for long-term immunity. (correct)

They provide immediate defense against all pathogens.

They initiate programmed cell death of plasma cells.

What is the role of effector cells in antibody-dependent cell cytotoxicity (ADCC)?

They produce antibodies against pathogens.

They bind to the Fc region of antibodies to mediate cell destruction. (correct)

They transport antigens to lymph nodes for presentation.

They enhance the activity of other immune cells.

During the resolution phase of the immune response, which process primarily ensures the elimination of excess immune cells?

Cellular differentiation

Inflammation

Phagocytosis

Apoptosis (correct)

Which type of immune cells are primarily responsible for the recognition of target cells in ADCC?

Natural killer (NK) cells Signup and view all the answers

What is one of the key benefits of the increased expression of cell surface molecules during memory formation?

It prepares B cells to respond more rapidly to future exposures. Signup and view all the answers

What is the primary role of memory T cells in the immune system?

To provide long-term immunity and quick response upon re-exposure Signup and view all the answers

Which molecules are primarily involved in the antigen presentation to T cells?

Major Histocompatibility Complex (MHC) Signup and view all the answers

What occurs during the effector phase of T cell function?

Effector T cells activate macrophages and neutrophils Signup and view all the answers

Which combination is correct regarding T cell differentiation?

Regulatory T cells help maintain immune tolerance Signup and view all the answers

Which of the following best describes co-stimulation in T cell activation?

Additional signals from APCs binding to T cell co-stimulatory receptors Signup and view all the answers

What is the fate of most effector T cells after the clearance of an infection?

They die through contraction by apoptosis Signup and view all the answers

Which statement regarding T cell receptor (TCR) binding is accurate?

TCR recognizes specific antigens presented by MHC molecules Signup and view all the answers

What triggers the release of cytokines during T cell activation?

Co-stimulation signals from additional receptors Signup and view all the answers

Which cytokine is primarily involved in promoting B cell maturation and the production of high-affinity antibodies?

Interleukin-21 (IL-21) Signup and view all the answers

What type of T helper cell is primarily involved in identifying intracellular bacteria such as Mycobacterium tuberculosis?

CD4+ Th1 Signup and view all the answers

In the context of HIV infection, what is the primary pathological consequence of the direct infection of CD4+ T cells?

Weakened cell-mediated immunity (CMI) Signup and view all the answers

Which of the following is a consequence of insufficient cell-mediated immunity in tuberculosis?

Bacterial escape from granulomas Signup and view all the answers

What is the role of cytotoxic T cells (CD8+) during viral infections?

Destroy infected cells Signup and view all the answers

Which cytokine is secreted by CD4+ Th1 cells to enhance the function of macrophages during a viral infection?

Interferon-gamma (IFN-γ) Signup and view all the answers

What type of memory T cells form as a result of prior exposure to pathogens?

Central memory T cells Signup and view all the answers

Which of the following processes is associated with the differentiation of T cells into effector and memory cells?

Cytokine signaling Signup and view all the answers

What mechanisms do effector CD8+ T cells employ to eliminate virus-infected cells?

Releasing cytotoxic granules Signup and view all the answers

Which type of T cell is characterized by the secretion of cytokines that primarily activate macrophages?

CD4+ Th1 Signup and view all the answers

What is required for full activation of T cells beyond antigen recognition?

Co-stimulation Signup and view all the answers

Which type of T cell directly kills infected or cancerous cells?

CD8+ cytotoxic T cells Signup and view all the answers

What molecules do CD8+ cytotoxic T cells use to kill their target cells?

Perforin and granzymes Signup and view all the answers

In the context of antigen presentation, which MHC class do CD4+ helper T cells recognize?

MHC Class II Signup and view all the answers

What is one of the main functions of CD4+ helper T cells after activation?

Secrete cytokines to activate other immune cells Signup and view all the answers

Which process describes the increase in number of activated T cells?

Clonal expansion Signup and view all the answers

What is the role of antigen-presenting cells (APCs) in T cell activation?

Presenting antigens in conjunction with MHC Signup and view all the answers

What characterizes memory T cells after an initial immune response?

They remain dormant and can respond to future infections Signup and view all the answers

Which type of T cell is primarily involved in skewing the immune response towards either cellular or humoral immunity?

CD4+ helper T cells Signup and view all the answers

Which cellular interaction is essential for co-stimulation during T cell activation?

T cell and APC interaction Signup and view all the answers

What is the primary role of T helper cells in the activation of B cells?

To provide signals that promote B cell activation. Signup and view all the answers

Which of the following processes significantly increases the affinity of antibodies produced by B cells for their specific antigens?

Somatic hypermutation Signup and view all the answers

In what location do mature naive B cells become activated upon encountering their specific antigen?

Germinal centers of lymphoid tissues Signup and view all the answers

What type of T cell is primarily responsible for aiding B cell activation?

T helper cells Signup and view all the answers

What occurs during clonal expansion of activated B cells?

B cells proliferate to generate large numbers of identical cells. Signup and view all the answers

Which statement about memory B cells is accurate?

They 'remember' specific antigens for future responses. Signup and view all the answers

Which mechanism allows B cells to change the class of antibody they produce?

Class switch recombination Signup and view all the answers

What can happen to B cells that strongly bind to self-antigens?

They undergo receptor editing or clonal deletion. Signup and view all the answers

What is the main function of plasma cells following activation of B cells?

To secrete large quantities of specific antibodies. Signup and view all the answers

During T cell activation, which signal is NOT typically necessary for full activation?

Direct contact with pathogens. Signup and view all the answers

Which phase of the immune response involves the multiplication of B cells to form a large population capable of responding to antigens?

Activation Phase Signup and view all the answers

What is the process called when B cells undergo a genetic rearrangement to produce various combinations of antibody coding DNA?

VDJ recombination Signup and view all the answers

Which mechanism allows antibodies to promote the destruction of pathogens by another immune cell type?

Opsonization Signup and view all the answers

During the immune response, what is the role of helper T cells in relation to B cells?

Providing activating signals through cytokines Signup and view all the answers

What key change occurs in B cells that become plasma cells during the effector phase?

They produce large amounts of antibodies Signup and view all the answers

What occurs when antibodies bind to pathogens during the neutralization process?

Pathogens block their ability to infect host cells Signup and view all the answers

In which phase do memory B cells play a crucial role following a subsequent encounter with the same antigen?

Secondary Immune Response Signup and view all the answers

What type of immune molecule do B cells primarily utilize to recognize a variety of antigens?

B Cell Receptors (BCRs) Signup and view all the answers

Which cytokine is essential for activating macrophages to enhance viral clearance during viral infections?

Interferon-gamma (IFN-γ) Signup and view all the answers

What is a primary characteristic of T follicular helper (Tfh) cells in relation to B cell function?

They support B cell maturation and the production of high-affinity antibodies. Signup and view all the answers

In tuberculosis, what immune response is triggered to contain the bacteria?

Generation of granulomas composed of immune cells. Signup and view all the answers

How does HIV particularly compromise the immune response in infected individuals?

By directly infecting and destroying CD4+ T cells. Signup and view all the answers

What is a significant consequence of insufficient cell-mediated immunity (CMI) in the context of tuberculosis?

Escape of bacteria from granulomas leading to active disease. Signup and view all the answers

What is the primary role of CD4 T helper cells in the immune response?

Enhance the activity of cytotoxic T cells and activate other immune cells Signup and view all the answers

Which cytokine is predominantly produced by Th1 cells to activate macrophages?

Interferon-gamma (IFN-γ) Signup and view all the answers

What is the primary function of cytokines produced by Th2 cells?

Stimulating eosinophil differentiation and B cell class switching Signup and view all the answers

Which of the following cytokines is involved in the recruitment of neutrophils by Th17 cells?

Interleukin-17 (IL-17) Signup and view all the answers

What is the primary role of T regulatory (Treg) cells in immune regulation?

Suppressing immune responses to maintain tolerance Signup and view all the answers

Which of the following is NOT a characteristic function of Th1 cells?

Promoting B cell class switching to IgE Signup and view all the answers

Which of the following cytokines is NOT typically produced by Th2 cells?

Interleukin-17 (IL-17) Signup and view all the answers

Which cell type is primarily responsible for maintaining the integrity of epithelial barriers during immune responses?

Th17 cells Signup and view all the answers

What is a significant consequence of excessive TNF-α production during an immune response?

Promotion of acute inflammation and tissue damage Signup and view all the answers

What is the effect of transforming growth factor-beta (TGF-β) on the immune system?

Promotes immune tolerance and suppresses immune activation Signup and view all the answers

What is the role of memory B cells after an initial immune response?

They provide long-term immunity by quickly responding to future infections with the same antigen. Signup and view all the answers

Which statement best describes the processes that occur after the pathogen is cleared from the body?

Effector B cells undergo apoptosis, leading to decreased immune activity. Signup and view all the answers

During antibody-dependent cell cytotoxicity (ADCC), what is the major role of the Fc receptors on effector cells?

To recognize and bind the Fc region of antibodies attached to target cells. Signup and view all the answers

What is a critical factor influencing the binding of antibodies to antigens during ADCC?

The structural conformation of the Fc region of the antibody. Signup and view all the answers

Which is NOT a characteristic of the resolution phase of the immune response?

Formation of new plasma cells for ongoing antibody production. Signup and view all the answers

Which type of antibody is primarily categorized as a pentamer?

IgM Signup and view all the answers

What is the outcome of programmed cell death (apoptosis) for effector B cells?

It decreases unnecessary immune activity and inflammation. Signup and view all the answers

What characterizes the memory B cell response upon re-encounter with the antigen?

A rapid and robust activation leading to quicker antibody production. Signup and view all the answers

Which immune cell type is primarily responsible for releasing cytotoxic molecules during ADCC?

Natural killer (NK) cells Signup and view all the answers

Which statement about the restoration of homeostasis following an immune response is true?

Memory B cells remain while excess immune cells are eliminated. Signup and view all the answers

What is the primary physiological effect of mast cell degranulation during anaphylaxis?

Increased vascular permeability leading to edema Signup and view all the answers

Which statement accurately describes the role of MHC molecules in T cell activation?

They help T cells recognize and differentiate between self and non-self antigens. Signup and view all the answers

Which type of T cell is characterized by its involvement in killing infected cells?

CD8+ cytotoxic T cells Signup and view all the answers

What is the primary function of activated CD4+ helper T cells?

Release cytokines to assist other immune cells. Signup and view all the answers

What role do co-stimulatory molecules play in T cell activation?

They provide essential signals beyond antigen recognition for full T cell activation. Signup and view all the answers

What distinguishes the differentiation of CD4+ helper T cells into various subsets?

The specific cytokines they release and respond to. Signup and view all the answers

How do cytotoxic T cells eliminate virus-infected cells?

By releasing perforin and granzymes to induce cell damage. Signup and view all the answers

What is the result of clonal expansion in T cells after activation?

Increased number of T cells specific for the recognized antigen. Signup and view all the answers

Why is the release of histamine during anaphylaxis critical?

It causes vasodilation and increased vascular permeability. Signup and view all the answers

What restricts the influence of auto-reactive B cells in autoimmune conditions like Graves' disease?

Regulatory T cells suppressing their activity. Signup and view all the answers

Study Notes

Cell Mediated Immunity

T cells recognize antigens presented by antigen-presenting cells (APCs), such as dendritic cells, macrophages, or infected cells.
CD8+ cytotoxic T cells recognize antigens presented by MHC Class I molecules.
CD4+ helper T cells recognize antigens presented by MHC Class II molecules.
Upon antigen recognition, T cells require a second signal for full activation, known as co-stimulation.
Activated T cells then proliferate (expand in number) through clonal expansion.
CD4+ helper T cells differentiate into various subsets while CD8+ cytotoxic T cells become capable of killing infected cells
- Th1 cells produce IFN-γ, activating macrophages to destroy intracellular bacteria.
- Th2 cells produce IL-4, IL-5, and IL-13, which activate B cells to produce antibodies and eosinophils.
- Th17 cells produce IL-17, which recruits neutrophils to fight infections and can cause inflammation.
- T regulatory cells suppress immune responses, preventing autoimmune reactions.
After the infection is cleared, most effector T cells undergo apoptosis, a process called contraction, to avoid an overactive immune response.
A small population of T cells becomes memory T cells, which persist long-term and are capable of quickly responding if the same pathogen is encountered in the future.

Pathogens that Initiate Cell Mediated Response

Viral infections
Bacterial infections

T Cell Activation

Antigen Presentation: APCs process and present antigens on their surface using molecules called major histocompatibility complexes (MHC).
- MHC Class I for cytotoxic T cells (CD8+).
- MHC Class II for helper T cells (CD4+).
Recognition: A T cell's receptor (TCR) recognizes and binds to the specific antigen-MHC complex on the APC. This is the first signal for activation.
Co-stimulation: To fully activate the T cell, a second signal is needed. This comes from additional molecules on the APC binding to co-stimulatory receptors on the T cell (like CD28).
Cytokine Signaling: Once the T cell is activated, APCs and other cells release cytokines, which help to guide the differentiation of the T cell into specific functional types.

T Cell Differentiation

CD8+ cytotoxic T cells directly kill infected cells by releasing cytotoxic molecules like perforin and granzymes.
CD4+ helper T cells secrete cytokines to activate other immune cells like macrophages, B cells, and additional T cells.
Memory T cells persist long-term and are capable of quickly responding if the same pathogen is encountered in the future.

Humoral Immunity

Humoral immunity relies on antibodies, which are proteins produced by B cells.
B cells differentiate into plasma cells, which secrete antibodies into the bloodstream.
Antibodies bind to antigens, neutralizing the pathogen.

B Cell Differentiation

B cells arise from stem cells in the bone marrow and mature in the bone marrow.
Immature B cells undergo a process called negative selection to remove B cells that recognize self-antigens, preventing autoimmune reactions.
B cells that strongly bind to self-antigens undergo one of the following:
- Receptor editing: The B cell attempts to rearrange its light chain again to change its BCR.
- Clonal deletion: The B cell is eliminated via apoptosis (programmed cell death).
- Anergy: The B cell becomes unresponsive and inactive.

Mature Naive B Cell Stage

Mature naive B cells express two classes of BCRs on their surface - IgM and IgD.
They circulate in the blood and lymphatic system awaiting activation by encountering their specific antigen.

Activation and Differentiation into Plasma Cells or Memory B Cells

When a mature naive B cell encounters an antigen that matches its BCR, it becomes activated with the help of T cells (specifically T helper cells) and other signals from the immune system.
Clonal expansion: The activated B cell proliferates and produces a large number of identical cells, all specific to the same antigen.
Class switch recombination: B cells can change the class of antibodies they produce without altering the antigen specificity of the BCR.
Somatic hypermutation: Mutations occur in the BCR genes, allowing for fine-tuning and increased affinity for the antigen.
Plasma cells produce large quantities of antibodies specific to the encountered antigen.
Memory B cells remain in the body for years, providing long-term immunity.

Isotypes

Monomer: IgD, IgE, IgG
Dimer: IgA
Pentamer: IgM

Antibody Dependant Cell Cytotoxicity (ADCC)

Antibodies (typically IgG) recognize and bind to antigens on the surface of target cells, such as cells infected with a virus or tumor cells.
Immune cells like natural killer (NK) cells, macrophages, or neutrophils have receptors on their surface called Fc receptors that bind to the Fc region of the antibody attached to the target cell.
Once the effector cell binds to the antibody, it is activated to release cytotoxic molecules, such as perforins and granzymes - directly killing the target cell.

### Defective Humoral Immune Response

Graves Disease:
- Autoreactive B cells produce thyroid-stimulating immunoglobulins, leading to hyperthyroidism.
Anaphylaxis:
- Mast cells loaded with IgE cause mast cell degranulation and histamine release.
- This leads to increased vasodilation, vascular permeability, a huge drop in blood pressure, and airway constriction.
Asthma:
- Mast cells in the airways release histamine, leading to bronchial constriction and increased secretion of fluid.
GFC:
- Immunoglobulin deficiency can lead to recurrent infections.
- GFC contains immunoglobulin and leukocytes, and they must be replaced regularly in patients with immunoglobulin deficiency.

Memory B Cells

Upon encountering the same antigen, memory B cells rapidly differentiate into plasma cells.
Plasma cells are antibody-secreting cells, leading to a robust immune response.

Antibody Structure

VDJ Recombination:
- Pro-B cells rearrange antibody-coding DNA before maturing into B cells, resulting in a broad range of antibody combinations.
B Cell Receptor (BCR) Recognition:
- BCRs bind to various antigens: proteins, polysaccharides, lipids, bacteria, and viruses.

Humoral Response: Activation, Effector, and Resolution Phases

Activation Phase

Antigen Recognition:
- B cells with specific BCRs bind to antigens matching their receptors.
Helper T Cell Involvement:
- Helper T cells (CD4+ T cells) recognize the same antigen and activate B cells via cytokine release.
Clonal Expansion:
- Activated B cells multiply, forming a large population of antigen-specific cells.
- A portion of these cells differentiate into plasma cells and memory B cells.

Effector Phase

Antibody Production:
- Plasma cells produce large amounts of specific antibodies (immunoglobulin).
Neutralization:
- Antibodies bind to pathogens, blocking their ability to infect cells.
Opsonization:
- Antibodies coat pathogens, marking them for destruction by phagocytes (macrophages and neutrophils).
Complement Activation:
- Antibodies activate the complement system, promoting inflammation and killing pathogens through the membrane attack complex (MAC).
Memory Formation:
- Memory B cells are generated, providing a faster and stronger response to future exposures of the same antigen.
Increased Expression of Cell Surface Molecules

Resolution Phase

Elimination of Excess Immune Cells:
- Most plasma cells and effector B cells undergo apoptosis, reducing inflammation and unnecessary immune activity.
Memory B Cells Remain:
- Memory B cells persist, providing long-term immunity.
Restoration of Homeostasis:
- The immune system returns to a balanced state, maintaining surveillance without harming the body's own tissues.

Antibody Isotypes:

Monomer: IgD, IgE, IgG
Dimer: IgA
Pentamer: IgM
Different isotypes are important in various stages of infection and immune challenges.

Antibody Dependent Cell Cytotoxicity (ADCC)

Antibody Binding:
- Antibodies (usually IgG) bind to antigens on target cells (e.g., virus-infected or tumor cells).
Effector Cell Recognition:
- Immune cells (NK cells, macrophages, neutrophils) possess Fc receptors that bind to the Fc region of the antibody attached to the target cell.
Target Cell Destruction:
- Effector cells release cytotoxic molecules (perforins and granzymes) to directly kill the target cell.
- NK cells play a primary role in ADCC.

Auto-reactive B Cells

Graves' Disease:
- Autoreactive B cells produce thyroid-stimulating immunoglobulins, leading to hyperthyroidism.

Anaphylaxis

Mast Cell Degranulation:
- Mast cells loaded with IgE undergo degranulation and release histamine.
Symptoms:
- Increased vasodilation, vascular permeability, a dramatic drop in blood pressure, and airway constriction causing epiglottis swelling.

Asthma

Mast Cells in Airways:
- Mast cells in airways with IgE lead to bronchial constriction and increased fluid secretion.

Gammopathy

Gamma Globulin Fraction (GFC):
- GFC contains IgM, IgG, IgA, leukocytes, and plasma.

Cell-Mediated Immunity (CMI)

Antigen Recognition:
- T cells recognize antigens presented by antigen-presenting cells (APCs) like dendritic cells, macrophages, or infected cells.
- T cell receptors (TCRs) bind to antigens presented in conjunction with major histocompatibility complex (MHC) molecules.
- CD8+ cytotoxic T cells recognize antigens presented by MHC Class I molecules.
- CD4+ helper T cells recognize antigens presented by MHC Class II molecules.
T Cell Activation:
- T cells require two signals for activation: antigen recognition and co-stimulation.
- Co-stimulatory molecules on APCs bind to receptors on T cells, providing the second signal.
- Activated T cells undergo clonal expansion.
- CD4+ helper T cells differentiate into subsets (Th1, Th2, Th17, Treg).
- CD8+ cytotoxic T cells become capable of killing infected cells.
T Cell Differentiation:
- T cells differentiate into effector T cells with specific functions:
  - CD8+ cytotoxic T cells directly kill infected or cancerous cells.
  - CD4+ helper T cells secrete cytokines to activate other immune cells.
Chemokine Signaling:
- Infected or damaged tissues release chemokines, attracting T cells to the affected area.
Adhesion and Migration:
- T cells adhere to blood vessel walls and migrate through the walls (extravasation) to enter the infected tissue.
Effector Function:
- T cells perform their specific immune functions, such as killing infected cells or helping other immune cells.

CD4+ vs. CD8+ T Cells

CD8+ T cells (Cytotoxic T cells):
- Kill cells via apoptosis.
CD4+ T cells (Helper T cells):
- Secrete cytokines to activate immune cells (macrophages, neutrophils, B cells), but do not directly kill cells.

CD4+ T Cell Subsets:

Th1 Cells:

Cytokines:
- Interferon-gamma (IFN-γ): Activates macrophages, enhances antigen presentation, and boosts cytotoxic T cell killing ability.
- Tumor necrosis factor-alpha (TNF-α): Promotes inflammation and helps eliminate intracellular pathogens.

Th2 Cells:

Cytokines:
- Interleukin-4 (IL-4): Promotes B cell class switching to IgE, important for allergic reactions and parasitic infections.
- Interleukin-5 (IL-5): Stimulates eosinophil growth and differentiation for fighting parasitic infections.
- Interleukin-13 (IL-13): Promotes IgE production and enhances mucus production in allergic responses.

Th17 Cells:

Cytokines:
- Interleukin-17 (IL-17): Induces production of pro-inflammatory cytokines and recruits neutrophils to fight extracellular pathogens.
- Interleukin-22 (IL-22): Maintains epithelial barrier integrity, promotes tissue repair, and enhances immune responses.

Treg Cells:

Cytokines:
- Interleukin-10 (IL-10): Suppresses immune responses, regulates inflammation, and prevents autoimmunity.
- Transforming growth factor-beta (TGF-β): Promotes immune tolerance, inhibits immune cell activation, and plays a role in tissue repair.

Tfh cells:

Cytokines:
- Interleukin-21 (IL-21): Promotes B cell maturation and differentiation, enhancing antibody production in lymph node germinal centers.

Applying CMI to Pathology

Viral Infections

Normal Role of CMI:
- Cytotoxic T cells (CD8+) identify and destroy virus-infected cells.
- Helper T cells (CD4+ Th1) secrete IFN-γ, activating macrophages and facilitating viral clearance.
Pathology Example:
- HIV directly infects and destroys CD4+ T cells, weakening CMI.
- This vulnerability leads to opportunistic infections.

Bacterial Infections

Normal Role of CMI:
- Th1 cells produce IFN-γ, activating macrophages to destroy intracellular bacteria (e.g., Mycobacterium tuberculosis).
Pathology Example:
- Tuberculosis (TB) involves granuloma formation (clusters of immune cells).
- Insufficient CMI allows bacteria to escape granulomas, resulting in active TB, tissue damage, and chronic inflammation.

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Description

Test your knowledge on cell mediated immunity and the role of T cells in recognizing antigens. This quiz covers CD8+ cytotoxic T cells and CD4+ helper T cells, their activation, and differentiation into various subsets. Explore how these cells respond to infections and maintain immune regulation.